That's the trouble David, there's no definition, so everyone can make a green claim. Unless you do your research you can be easily duped by someone selling you green. Also, the "green" certifiers will use whatever is important to them to give their approval, and if you aren't pouring your waste into the river those criteria don't matter.
Since Brent mentioned bamboo shirts, I'll use bamboo fabric as an example of how we can be fooled. The following is copied from a bamboo fabric website. You'll find similar creative text on many green sites.
We sell fabric that's spun and knit from long, strong, soft fibers derived from the pulp bamboo plants. Read on about this fabric's environmental and health benefits, practicality and comfort.
On Bamboo Fabric and the Environment
Many of our customers order our fabrics for applications in place of cotton because of its absorbency and comfort against the skin. (OK)
Cotton is one of the most intensely sprayed crops in the world, and cotton pesticides are the greatest crop contributor to volatile organic compounds in the environment. Cotton requires wide spacing to grow, allowing bare soil to oxidize in the sun, releasing carbon into the atmosphere, allowing rain to wash soil and chemicals into stream, and decreasing soil fertility. Cotton fabrics, including those made from organic cotton raw material and labeled "organic," commonly go through a series of finishing processes involving synthetic resins, amylase enzyme, Kier boiling, detergents and alkaline solutions, and that's not including bleaches and brighteners used to alter color and caustic soda used in mercerization. (OK, lots of BS here about that other natural fabric; cotton. Some of this is true, in some countries, for some processes, sometimes, but it doesn't apply to all cotton production everywhere.)
Bamboo, on the other hand, takes in five times the volume of greenhouse gasses as an equivalent stand of timber trees and releases 35% more oxygen. It needs no replanting, pesticides or fertilizers, and its roots retain water in the watershed, sustaining riverbanks and reducing water pollution. The bamboo used to make most of the fabrics we currently stock is certified organically grown by OCIA. (Fine so far)
It is processed via a type of viscose process involving caustic soda, and then washed with water. (This is the sentence that unravels the hooey. Viscose is process used to make rayon, and is commonly used as a weasel word to avoid saying RAYON. The fabric isn't bamboo, it's rayon derived from bamboo. They also mention caustic soda, as if this is something you bathe your baby in, and don't mention where all the caustic soda and rinse water go. In Asian countries where bamboo is grown, it goes right into the sea. Not so green anymore, eh? Don't mention it, because after all they're just selling green, not being green.)